The present invention relates to a coated cutting tool insert with a sharp cutting edge particularly useful for machining of non-ferrous materials such as titanium, aluminium, brass, bronze, plastics etc.
For the machining of metals, cutting tool inserts of cemented carbide having a rake face and clearance faces intersecting to form a cutting edge are used. The cutting edge should be sharp to provide low cutting forces and low energy consumption. However, cemented carbide is a brittle material and for that reason, a sharp cutting edge is generally not strong enough. If it breaks, the cutting forces increase and the surface finish of the machined material will be poor. In order to strengthen the edge it can be rounded to a radius of generally 10-50 μm, or provided with a chamfer or a land. The exact design of the edge depends on the material to be machined and is a compromise between acceptable cutting forces and strength of the edge. Some workpiece materials such as aluminium, etc., require a very sharp edge with minimal edge rounding. An excessively rounded edge can in such materials represent a worn edge and can affect the subsequent wear development. For the machining of such materials, uncoated cemented carbide inserts are generally used. If a coating is applied, the edge will be less sharp. In addition, coated cutting edges require a certain amount of rounding to ensure a satisfactory application of a coating. It is however, a desire to be able to use coated inserts also for the machining of materials requiring sharp cutting edges.
Published U.S. Patent Application 2002/0187370 disclose the grinding of certain amounts of the rake face and flank side of a blade-edge ridge to achieve a surface roughness of 0.2 μm or less over a reference length of 5 μm. It is stated that surface reforming by means of microblasting and ion-beam radiation may also be applied but only grinding and lapping are exemplified.